Hybrid electric vehicle and method of controlling regenerative braking therefor

Abstract

A hybrid electric vehicle capable of more efficient regenerative braking and a regenerative braking control method therefor are provided. A method for controlling regenerative braking of a hybrid electric vehicle may include: determining, when a braking request occurs, a state of an engine clutch configured to selectively connect a first motor directly connected to an engine and a second motor directly connected to an input end of a transmission; determining, when the engine clutch is in an opened state, whether or not to engage the engine clutch in order to perform additional regenerative braking by using the first motor; and performing regenerative braking based on whether or not to engage the engine clutch.

What is claimed is: 
     
         1 . A method for controlling regenerative braking of a hybrid electric vehicle, the method comprising:
 determining, in response that a braking request occurs, a state of an engine clutch configured to selectively connect a first motor directly connected to an engine and a second motor directly connected to an input end of a transmission;   determining, in response that the engine clutch is in an opened state, whether or not to engage the engine clutch in order to perform additional regenerative braking by using the first motor; and   performing regenerative braking based on whether or not to engage the engine clutch.   
     
     
         2 . The method according to  claim 1 ,
 wherein determining whether or not to engage the engine clutch comprises determining whether preset engine clutch engagement conditions are satisfied or not.   
     
     
         3 . The method according to  claim 2 ,
 wherein the preset engine clutch engagement conditions comprise a driving load condition according to whether or not energy recovery is possible and a state of charge of a battery.   
     
     
         4 . The method according to  claim 2 ,
 wherein the preset engine clutch engagement conditions comprise:
 an engine stall prevention condition according to engine revolutions per minute (RPM) when the engine clutch is engaged; and 
 a regenerative braking early-termination prevention condition according to a vehicle speed. 
   
     
     
         5 . The method according to  claim 2 ,
 wherein the preset engine clutch engagement conditions comprise:
 a residual torque condition for residual torque capable of being executed by the additional regenerative braking using the first motor in a regenerative braking allowance according to the braking request; and 
 a charging power limit condition according to a charge amount of the second motor during the additional regenerative braking and a charging power limit of a battery. 
   
     
     
         6 . The method according to  claim 5 ,
 wherein the preset engine clutch engagement conditions further comprise a consumption energy condition according to a predicted power of the first motor during the additional regenerative braking and an engagement consumption power for speed synchronization of the engine and the second motor.   
     
     
         7 . The method according to  claim 6 , further comprising:
 determining the predicted power to be a smallest value among a value obtained by subtracting the charge amount of the second motor from the charging power limit of the battery, a value obtained by multiplying a value obtained by subtracting a torque of the second motor and a friction torque of the engine from the regenerative braking allowance according to the braking request by RPM of the second motor, and a charging power limit of the first motor; and   predetermining a value of the engagement consumption power by using a speed difference between the engine and the second motor as a factor.   
     
     
         8 . The method according to  claim 5 ,
 wherein the preset engine clutch engagement conditions further comprise a consumption energy condition according to a predicted charging energy of the first motor during the additional regenerative braking and an engagement consumption energy for speed synchronization of the engine and the second motor.   
     
     
         9 . The method according to  claim 2 , further comprising:
 performing control, when all of the preset engine clutch engagement conditions are satisfied, to engage the engine clutch and perform regenerative braking by using both the first motor and the second motor.   
     
     
         10 . The method according to  claim 9 ,
 wherein performing the control comprises:
 controlling a charging power of the first motor to be a value obtained by subtracting a charging power of the second motor from a charging power limit of a battery; and 
 controlling a torque of the first motor to be a value obtained by subtracting a torque of the second motor and a friction torque of the engine from a regenerative braking allowance according to the braking request. 
   
     
     
         11 . A hybrid electric vehicle comprising:
 an engine;   a first motor directly connected to the engine;   an engine clutch having a first end connected to the first motor;   a second motor connected to a second end of the engine clutch and configured to be selectively connected to the first motor through the engine clutch;   a transmission having an input end directly connected to the second motor; and   a controller configured to:
 determine, in response that a braking request occurs, a state of an engine clutch, 
 determine, in response that the engine clutch is in an opened state, whether or not to engage the engine clutch in order to perform additional regenerative braking by using the first motor, and 
 control regenerative braking to be performed based on whether or not to engage the engine clutch. 
   
     
     
         12 . The hybrid electric vehicle according to  claim 11 ,
 wherein the controller is further configured to determine whether preset engine clutch engagement conditions for engaging the engine clutch are satisfied or not.   
     
     
         13 . The hybrid electric vehicle according to  claim 12 ,
 wherein the preset engine clutch engagement conditions comprise a driving load condition according to whether or not energy recovery is possible and a state of charge of a battery.   
     
     
         14 . The hybrid electric vehicle according to  claim 12 ,
 wherein the preset engine clutch engagement conditions comprise:
 an engine stall prevention condition according to engine RPM when the engine clutch is engaged; and 
 a regenerative braking early-termination prevention condition according to a vehicle speed. 
   
     
     
         15 . The hybrid electric vehicle according to  claim 12 ,
 wherein the preset engine clutch engagement conditions comprise:
 a residual torque condition for residual torque capable of being executed by the additional regenerative braking using the first motor in a regenerative braking allowance according to the braking request; and 
 a charging power limit condition according to a charge amount of the second motor during the additional regenerative braking and a charging power limit of a battery. 
   
     
     
         16 . The hybrid electric vehicle according to  claim 15 ,
 wherein the preset engine clutch engagement conditions further comprise a consumption energy condition according to a predicted power of the first motor during the additional regenerative braking and an engagement consumption power for speed synchronization of the engine and the second motor.   
     
     
         17 . The hybrid electric vehicle according to  claim 16 ,
 wherein the controller is further configured to:
 determine the predicted power to be a smallest value among a value obtained by subtracting the charge amount of the second motor from the charging power limit of the battery, a value obtained by multiplying a value obtained by subtracting a torque of the second motor and a friction torque of the engine from the regenerative braking allowance according to the braking request by RPM of the second motor, and a charging power limit of the first motor, and 
 predetermine a value of the engagement consumption power by using a speed difference between the engine and the second motor as a factor. 
   
     
     
         18 . The hybrid electric vehicle according to  claim 15 ,
 wherein the preset engine clutch engagement conditions further comprise a consumption energy condition according to a predicted charging energy of the first motor during the additional regenerative braking and an engagement consumption energy for speed synchronization of the engine and the second motor.   
     
     
         19 . The hybrid electric vehicle according to  claim 12 ,
 wherein the controller is further configured to perform control, when all of the preset engine clutch engagement conditions are satisfied, to engage the engine clutch and perform regenerative braking by using both the first motor and the second motor.   
     
     
         20 . The hybrid electric vehicle according to  claim 19 ,
 wherein the controller is further configured to:
 control a charging power of the first motor to be a value obtained by subtracting a charging power of the second motor from a charging power limit of a battery; and 
 control a torque of the first motor to be a value obtained by subtracting a torque of the second motor and a friction torque of the engine from a regenerative braking allowance according to the braking request.